Midi to CV/Gate Converter, help please

[truzz]

Hello folks,

A few days ago I decided to mount this Midi to CV/Gate Converter.

Unfortunately it doesn't work.
The PIC seems to work, as the LED blinks at startup (3 long, followed by short blinks, then lights off).
If I press the learn/mode switch, the LED remains lit, waiting for the midi message.
So it seems it never receives any message.

I checked the input, at both pin 4 and 5 of midi connector:
biased to 5 volts, straight line when no notes are played, short (negative going) pulses when Logic is playing notes.
The output of the optocoupler (pin 6), stays high (~ 5V), and I'm not seeing any pulse, even when the  notes are played.
Always straight line to 5 volts.

I'm afraid I've fried the coupler, or this is normal?

Any test I could make with a simple transformer? (I was thinking of momentarily remove the opto, feeding PIC's input from the sec of a transformer), just to see if the rest of the circuit behaves as it should.

Is this a good idea to test? Should I hook up the trafo sec. to +5V?

I'm a newbie about PICs and MIDI, any help greatly appreciated.

Thanks in advance.

 

[truzz]

uhm.... cool project, but I'm stuck.
No output. Don't know how to check if pic is working as it should.

Any successful builder?
Plz help. Thanks.

 

[hobiesound]

might sound like a stupid question, but i don't see the code or the firmware for the pic anywhere. Did you upload a code of sorts to the pic?

Also the midi signal is not possible to read with a multimeter since it's a fast ac signal and otherwise it's a fixed dc when idle. you need either a scope or a logic-analyser to read it.

greetings,

Thomas

 

[s2udio]

might sound like a stupid question, but i don't see the code or the firmware for the pic anywhere.

My first thought
Yup the files are there (bottom of page)...... but
Did it come as a kit (pre programed pic)  ?
If not you need a pic programer.

If programmed.......... then a scope may be nessesary as per hobiesound stated

 

[truzz]

Hi,
thanks for the replies. Yes, I'm using a scope, and I can see the pulses at the Midi input, but only the 5V straight line at opto output and pic input. Not sure if this is normal.

I've also mounted a completely different circuit (this one for your reference).
Mounted a brand new optocoupler (6N136), and a new pic (16F628 20/p). The other was the 628A version, on the first project build.

But nothing, the same problem.
The LED blinks 3 times, then off (so I guess the pic received the hex file).
I programmed the pic with PICkit2, the HEX files are on the respective sites.
I did the verification on pickit and it was successful.

Uhm, what am I doing wrong? Am I missing something?
I'm using an old Logic (4.8.1) on a Mac, with the MIDI output from Digi 001.

Anyone?

 

[s2udio]

Hi,
thanks for the replies. Yes, I'm using a scope, and I can see the pulses at the Midi input, but only the 5V straight line at opto output and pic input.

No input data then.
Are there  pulses at pin 7.........RB1 of the pic ?
Or pin 6 of the opto..... ?
VCC and VDD in the correct place ?
Are you using stripboard ?
Power down and remove the Pic...then see if you have data at the input.
What you doing with pin 7 of the opto.

 

[obsoletetechnology]

Hi, I am the originator of this midi/cv module and just stumbled into this forum...
To the problems you are experiencing:
Your code seems to be running fine on the uC, the led flashing usually means that the code is running well.

I would suggest 2 things, one would be the wiring of the midi connector, the schematic actually shows the DIN connector from the rear. The fact you do not have a signal at the output of the optocoupler would be an indication for this.
Second is the decoupling capacitors for the opto, in some designs I've seen the opto going into oscillation without a good decoupling of the DC.

hope this is of some help,
Obsoletetechnology

 

[truzz]

Hi,
thanks everyone for the replies.

Hi, I am the originator of this midi/cv module and just stumbled into this forum...
I would suggest....
the wiring of the midi connector, the schematic actually shows the DIN connector from the rear. The fact you do not have a signal at the output of the optocoupler would be an indication for this.

hope this is of some help,
Obsoletetechnology

hi Obsoletetechnology,
much respect for your useful project, it is really handy, and:
yes, the communication problem was due to uncorrect midi pinout, your schematic diagram still indicating pin 4 &5 swapped.

Furthermore:
It doen't seem to track properly.
The MIDI reads only from C0 to B3 (C4 not included, it doesn't read C4 ?!)

With the best tracking I can get, I can read these voltages:

C0 : 0.51V
C1:  1.00V
C2:  2.00V
C3:  4.00V (should be 3.00V)

I can read 3V at G2.
Very strange.
Cannot track better than this.

What might be the cause?
Any suggestion?

Thank you.

 

[obsoletetechnology]

Hi,
It seems that you're almost done!
Your module is obviously in Logarithmic mode, if you to hold the button pressed while powering up it will switch to linear mode.

Hope this helps,
Obsoletetechnology
http://obsoletetechnology.wordpress.com/

ps. could you post a pic of your finished module?

 

[truzz]

Ok, it was in log mode. Your help was precious!

It tracks a lot better now, even though not perfect. Will try to improve later.

Maybe a +/- PSU will improve things (C0 never reach exactly 0.00V).

Pic:
here you are.

Thank you and happy new year!
8)

 

[gyraf]

Looks like a very nice and usable project indeed.

And thanks for stopping by and helping, Obsoletetechnology!

Jakob E.

 

[obsoletetechnology]

@truzz:
glad it's working now. to the non-linearity: did you follow the calibration procedure for the offset and gain?

@gyraf:
my pleasure!